IDAX AND MIDAX printing techniques are commercial electrographic imaging techniques that utilize what is referred to as silent electric discharge. In such systems, an ion cartridge is mounted adjacent an imaging drum. The drum then moves into contact with a transfer sheet (e.g. paper). The conventional cartridges utilized in these printing systems include first and second electrodes, typically called the driver and control electrodes, separated by a solid dielectric member, such as a sheet of mica. The control electrode, typically in the form of control fingers, defines an edge surface disposed opposite the driver electrode to define a discharge region at the junction of the edge surface and the solid dielectric member. An alternating potential is applied between the driver and control electrodes of sufficient magnitude to induce charged particle producing electrical discharges in the discharge region, and means are provided for applying a charged particles extraction potential between the control electrode and a further electrode, so that imaging occurs on the imaging drum, or dielectric paper or like dielectric moving past the ion cartridge. In most commercial installations a screen electrode is also provided, between the imaging drum and the control electrode, and separated by an insulating spacer from the control electrode. A commercial ion cartridge is typically constructed of a plurality of driver, control, and screen electrode units, in a matrix form.
In co-pending application Ser. No. 07/530,358 filed May 31, 1990, and in U.S. Pat. No. 4,918,468 (the disclosure of which is hereby incorporated by reference herein) in order to extend cartridge life, that is significantly put off ion cartridge failures that are euphemistically referred to as "red death", "white death", and "black death", a control gas, such as nitrogen, is supplied into the discharge region of the cartridge, and is injected from within the cartridge structure, creating a pure positive outflow of the gases from the cartridge. Even when the outflow is pure compressed air, it eliminates all electrically neutral internal gaseous contaminants from the plant environment (such as gases which cause ammonium nitrate and thus "white death"), and helps to deter contamination by uncontrolled toner particles (with resulting "black death").
The mechanism by which the gas is injected, according to the present invention, ensures optimum results. According to the present invention, a controlled gas (such as compressed air, but more preferably nitrogen, noble gases, or mixtures of noble gases or noble gases with nitrogen) is supplied to the discharge site or region, the discharge region having first and second control fingers (electrodes) each having first and second ends and a plurality of active openings therein at which active openings the discharges are formed. The controlled gas is supplied through first and second gas input channels are provided for each pair (the first and second) of control fingers, each gas input channel connected to either the first ends or the second ends of both the control fingers. Of course as many pairs of control fingers are provided as are necessary to provide a cartridge of desired size.
While the gas supply system described above is very beneficial, and effective, for some controlled gases, such as nitrogen, the charge output associated with the active openings and the control fingers is very uneven, being very high near the ends, and very low in the middle. Such unevenness is unacceptable, producing poor print quality, manifested in regularly spaced bands of alternating dark and light print regions which are easily recognized by the eye and which also produce machine scanned errors because of the uneveness. However according to the invention it is possible to stabilize the charge output so that there is a substantially even distribution of charge output along the length of each control finger. This is accomplished by providing first and second bleed holes associated with each of the first and second control fingers closer to the first and second gas input channels, respectively, than are the active openings in the control fingers. The bleed holes are preferably provided in a screen electrode overlying the control fingers, and having openings therein corresponding to (and substantially the same size as) the active openings in the control fingers. Where a single bleed hole is provided at each end of each control finger, and sixteen active openings are provided in each control finger, each of the bleed holes preferably has a surface area of approximately three times that of a single active opening.
It has also been surprisingly found that the cartridge output is enhanced slightly even with the injection of high pressure plain compressed air as the controlled gas when utilizing the bleed hole system and the control fingers, according to the invention. It has been suggested that such a phenomena may indicate that the positive outward flow of any gas, such as air, nitrogen, noble gases, or mixtures of each, alters the characteristics of charge extraction of the electrical fields determined by the control finger electrode, the screen electrode, and the dielectric imaging surface.
The invention also contemplates a method of generating charged particles for electrostatic imaging using a solid dielectric and first and second electrodes, with a discharge region. The method comprises the steps of: (a) Applying an alternating potential between the first and second electrodes to induce charged particle producing electrical discharges in the discharge region between the solid dielectric member and the first electrode. (b) Applying a charged particle extraction potential between the second electrode and a further member to extract charged particles produced by the electrical discharges. (c) Applying the external charged particles to a further member to form an electrostatic image. And, (d) supplying a controlled gas to the discharge site from opposite ends of the second electrode in such a manner as to stabilize the charge output so that it is substantially even along the discharge site.
The invention also comprises a silent electric discharge ion generating system including an ion discharge region including first and second control fingers each having first and second ends and a plurality of active openings therein, the ion discharges taking place at the edges of the active openings. The system comprises: Means for supplying controlled gas to the discharge site to displace at least some of the air at the discharge site during the generation of charged particles. The gas supplying means comprise first and second gas input channels, each connected to either the first ends or the second ends of the control fingers; and, means for stabilizing the charge output associated with the active openings in the control fingers so that there is a substantially even distribution of charge output along the length of each control finger.
It is the primary object of the present invention to provide for the effective extension of cartridge life for MIDAX printers, with good print quality. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.